1. Field of the Invention
The present invention relates to a method of fabricating a dynamic random access memory (DRAM), and especially a method of fabricating a DRAM that simplifies fabricating processes.
2. Description of Related Art
DRAMs use capacitors to store information. Data content of each memory cell is read by judging charges stored in the capacitor. Sizes for present memory cells are very small. In order to increase capacitance of the capacitors to reduce possibility of error reading on data, and to further reduce refreshing frequencies to increase operation efficiency, a usual way is increasing surface areas of lower electrodes of the capacitors. By increasing the surface areas of the capacitors, sufficient storage capacitance is thereby provided. In order to satisfy requirements of the surface areas of the capacitors and of integration of the memory cells, trench capacitors have become a popular choice.
In order to enhance integration of the DRAMs, in circuit design two passing gates pass a top of the trench capacitor, and an isolation structure is used to isolate the passing gates and the trench capacitor. In prior art, a method of forming the isolation structures comprises, for example, forming a complex isolation structure comprising silicon oxide/silicon nitride on the trench capacitor.
However, the complex isolation structure comprising silicon oxide/silicon nitride requires up to 20 complex steps such as disposition of silicon oxide and silicon nitride, using a mask to form a patterned photoresist layer, using the patterned photoresist layer to etch a film of the silicon nitride, wet etching of the film of the silicon oxide, washing steps and various sorts of inspection steps. Therefore a problem of complex processes arises.